JP2015231762A - Run-flat radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a run-flat radial tire which can suppress the occurrence of a buckling phenomenon at a tire side part at run-flat traveling.SOLUTION: A tire 10 has: a carcass 14; an inclined belt layer 16 constituted of belt plies 16A, 16B which are arranged outside a tire radial direction of the carcass 14; a tread part 20 in which a plurality of circumferential main grooves 21 are formed at a tread; and a side reinforcing rubber layer 24 which is arranged at a tire side part 22, located inside the tire rather than the carcass 14, extends to the tread part 20 side from a bead part 12, and reinforces the tire side part 22. When setting a distance from an end part 16AE of the belt ply 16A having a maximum width up to an opening edge 21AE of the circumferential main groove 21A along a tire width direction as A[mm], a width of the belt ply 16A as B[mm], and a groove depth of the circumferential main groove 21A as C[mm], a relationship of A/B>0.025×C+0.06 is satisfied.

Description

  The present invention relates to a run-flat radial tire that can safely travel a certain distance even when the internal pressure is reduced due to puncture or the like.

  A side-reinforced run-flat radial tire in which a tire side portion is reinforced with a side reinforcing rubber is known (see, for example, Patent Document 1).

JP 2012-116212 A

  By the way, in the side-reinforced run-flat radial tire, when SA (slip angle) is given by turning the vehicle or the like when running with the internal pressure reduced (run-flat running), the tire side portion There may be a buckling phenomenon in which the tire bends inside the tire.

  An object of this invention is to provide the run flat radial tire which can suppress that a buckling phenomenon generate | occur | produces in a tire side part at the time of run flat driving | running | working.

  A run-flat radial tire according to a first aspect of the present invention includes a carcass straddling between a pair of bead portions, and a cord provided on the outer side in the tire radial direction of the carcass and extending in a direction inclined with respect to the tire circumferential direction. An inclined belt layer formed of at least one belt ply; a tread portion provided on the outer side in the tire radial direction of the inclined belt layer; and a plurality of circumferential main grooves extending in the tire circumferential direction on the tread surface; and the bead A side reinforcement layer that is provided on a tire side portion that connects the portion and the tread portion, is located on the tire inner side than the carcass, extends from the bead portion side to the tread portion side, and reinforces the tire side portion; An opening on the outer side in the tire width direction of the circumferential main groove on the outermost side in the tire width direction from an end portion on the outer side in the tire width direction of the belt ply with the maximum width A distance along the tire width direction to the portion is A [mm], the width of the belt ply of the maximum width is B [mm], and the groove depth of the circumferential main groove on the outermost side in the tire width direction is C [mm] The relationship of A / B> 0.025 × C + 0.06 is satisfied.

  In the run flat radial tire according to claim 1, since the relationship of A / B> 0.025 × C + 0.06 is satisfied, for example, compared with a tire that does not satisfy the above relationship, a tread end portion (tread portion tire) The bending rigidity in the vicinity of the end in the width direction is increased. Thereby, even if SA is given at the time of run-flat traveling, the vicinity of the tread end portion is unlikely to be bent, and the occurrence of a buckling phenomenon at the tire side portion starting from the vicinity of the tread end portion can be suppressed.

  The run-flat radial tire according to claim 2 of the present invention is the run-flat radial tire according to claim 1, wherein the side reinforcing layer has a tire width of the belt ply whose end on the tread portion side has a maximum width. It is located on the inner side in the tire width direction than the end portion on the outer side in the direction.

  In the run-flat radial tire according to claim 2, since the end portion on the tread portion side of the side reinforcing layer is positioned on the inner side in the tire width direction with respect to the end portion on the outer side in the tire width direction of the maximum width belt ply, The end of the reinforcing layer on the tread portion side overlaps the belt ply having the maximum width. As described above, the end portion of the side reinforcing layer on the tread portion side overlaps the belt ply having the maximum width, whereby the bending rigidity in the vicinity of the tread end portion is improved and the occurrence of the buckling phenomenon in the tire side portion is suppressed.

  Here, when the end of the side reinforcing layer on the tread portion side is overlapped with the belt ply with the maximum width, the tread portion extends in the tire width direction starting from the groove bottom of the circumferential main groove on the outermost side in the tire width direction during run flat running. Bending may cause excessive tensile force to act on the inner surface of the side reinforcing layer corresponding to the vicinity of the end of the maximum width belt ply. However, when the relationship of A / B> 0.025 × C + 0.06 is satisfied, the distance A from the end of the maximum width belt ply to the opening edge of the outer circumferential main groove on the outermost side in the tire width direction Since the groove depth C of the circumferential main groove is regulated, the tread portion is less likely to bend in the tire width direction starting from the groove bottom of the circumferential main groove (the bending is suppressed), and the end of the maximum width belt ply It is possible to suppress an excessive tensile force from acting on the inner surface of the side reinforcing layer corresponding to the vicinity. Thereby, durability of the side reinforcement layer at the time of run flat running can be improved, suppressing generation | occurrence | production of the buckling phenomenon of a tire side part as mentioned above.

  The run-flat radial tire according to claim 3 of the present invention is the run-flat radial tire according to claim 1 or 2, wherein the tire cross-section height is 115 mm or more.

  In the run flat radial tire according to claim 3, the run flat radial tire having a tire cross-section height (section height) of 115 mm or more has a tire side portion that is easily bent. However, the occurrence of the buckling phenomenon can be suppressed.

  The run flat radial tire of the present invention can suppress the occurrence of a buckling phenomenon at the tire side portion during run flat running.

It is a half sectional view showing one side of a cut surface which cut a run flat radial tire concerning an embodiment of the present invention along the tire width direction. It is sectional drawing cut | disconnected along the tire width direction which shows the state at the time of turning in the run flat driving | running | working of the run flat radial tire which concerns on embodiment of this invention. It is a graph which shows the relationship between the rim | limb removal parameter | index inside a turning of a vehicle, and the rim | limb removal parameter | index outside a turning. It is a graph which shows the relationship between the ratio Y and the groove depth C in a test example.

Hereinafter, an embodiment of a run flat radial tire of the present invention will be described with reference to the drawings.
FIG. 1 shows one side of a cut surface cut along the tire width direction of a run-flat radial tire 10 (hereinafter referred to as “tire 10”) of the present embodiment. In the drawing, the arrow TW indicates the width direction (tire width direction) of the tire 10, and the arrow TR indicates the radial direction (tire radial direction) of the tire 10. The tire width direction here refers to a direction parallel to the rotation axis of the tire 10. The tire radial direction refers to a direction orthogonal to the rotation axis of the tire 10. Reference sign CL indicates the equator of the tire 10 (tire equator).

  In the present embodiment, the side closer to the rotation axis of the tire 10 along the tire radial direction is “inner side in the tire radial direction”, and the side farther from the rotation axis of the tire 10 along the tire radial direction is “outer side in the tire radial direction”. It describes. On the other hand, the side close to the tire equator CL along the tire width direction is described as “inner side in the tire width direction”, and the side far from the tire equator CL along the tire width direction is described as “outer side in the tire width direction”.

  FIG. 1 shows the tire 10 when mounted on a standard rim 30 (indicated by a two-dot chain line in FIG. 1) and filled with standard air pressure. Here, the “standard rim” refers to a rim defined in the Year Book 2014 version of JATMA (Japan Automobile Tire Association). The standard air pressure is the air pressure corresponding to the maximum load capacity of the Year Book 2013 version of JATMA (Japan Automobile Tire Association).

  In the following explanation, the load is the maximum load (maximum load capacity) of a single wheel at the applicable size described in the following standard, and the internal pressure is the maximum load of a single wheel described in the following standard. The rim refers to a standard rim (or “Applied Rim” or “Recommended Rim”) in an applicable size described in the following standard. The standards are determined by industry standards that are valid in the region where the tire is produced or used. For example, in the United States, “The Tire and Rim Association Inc. Year Book”, in Europe “The European Tire and Rim Technical Standards Standards” in the Japan Automobile Association of Japan Has been.

  As shown in FIG. 1, the tire 10 includes a pair of left and right bead portions 12 (in FIG. 1, only one bead portion 12 is illustrated), a carcass 14 straddling a pair of bead portions 12 in a toroid shape, and a carcass 14. An inclined belt layer 16, a belt reinforcing layer 17 and a reinforcing cord layer 18 provided on the outer side in the tire radial direction, and a tread portion provided on the outer side in the tire radial direction than the inclined belt layer 16 and constituting the outer peripheral portion of the tire 10. 20, a tire side portion 22 that connects the bead portion 12 and the tread portion 20, and a side reinforcing rubber layer 24 provided on the tire side portion 22. Note that the tire side portion 22 of the present embodiment includes a sidewall portion 22A on the bead portion 12 side and a shoulder portion 22B on the tread portion 20 side.

  In the tire 10 of the present embodiment, the tire cross-section height (section height) SH is set to 115 mm or more. The “tire cross-section height SH” here refers to a length that is ½ of the difference between the tire outer diameter and the rim diameter when the tire 10 is assembled to the standard rim 30 and the internal pressure is the standard air pressure. . Moreover, in this embodiment, although the tire cross-section height SH of the tire 10 is set to 115 mm or more, this invention is not limited to this structure, You may set the tire cross-section height SH lower than 115 mm. . As an example, in the present embodiment, the tire size of the tire 10 is 215 / 60R17.

  A bead core 26 is embedded in each of the pair of bead portions 12. The carcass 14 straddles these bead cores 26.

  The carcass 14 is constituted by one or a plurality of carcass plies, and the carcass ply is formed by coating a plurality of cords (for example, an organic fiber cord or a metal cord) with a covering rubber. The carcass 14 formed in this manner extends from one bead core 26 to the other bead core 26 in a toroid form, thereby constituting a tire skeleton. Further, the end portion side of the carcass 14 is locked to the bead core 26. Specifically, the end portion of the carcass 14 is folded and locked around the bead core 26 from the inner side in the tire width direction to the outer side in the tire width direction. Further, the folded end portion 14 </ b> A of the carcass 14 is disposed in the tread portion 20. In the present embodiment, the end portion 14A of the carcass 14 is arranged in the tread portion 20. However, the present invention is not limited to this configuration, and the end portion 14A of the carcass 14 is arranged in the tire side portion 22. It is good.

  A bead filler 28 extending from the bead core 26 to the outer side in the tire radial direction is embedded in a region surrounded by the carcass 14 of the bead portion 12. The bead filler 28 decreases in thickness toward the outer side in the tire radial direction.

An inclined belt layer 16 is disposed outside the carcass 14 in the tire radial direction. The inclined belt layer 16 is composed of one or a plurality of belt plies. The belt ply is formed by covering a plurality of cords (for example, an organic fiber cord, a metal cord, etc.) with a covering rubber. The cord constituting the belt ply extends in a direction inclined with respect to the tire circumferential direction. Note that the inclined belt layer 16 of the present embodiment is composed of two belt plies 16A and 16B.
The belt ply 16A is disposed on the inner side in the tire radial direction of the belt ply 16B. Further, the belt ply 16A has a width (length) along the tire width direction wider (longer) than a width (length) along the tire width direction of the belt ply 16B. The belt ply 16A of the present embodiment is an example of the maximum width belt ply of the present invention.

  A belt reinforcing layer 17 is provided outside the inclined belt layer 16 in the tire radial direction. The belt reinforcing layer 17 covers the entire inclined belt layer 16. A pair of reinforcing cord layers 18 are provided outside the belt reinforcing layer 17 in the tire radial direction so as to cover both ends of the belt reinforcing layer 17. The reinforcing cord layer 18 is formed by arranging a plurality of cords (for example, organic fiber cords, metal cords, etc.) that are inclined in the range of 60 to 90 degrees with respect to the tire circumferential direction in parallel. In the present embodiment, as an example, PET is used as a cord constituting the reinforcing cord layer 18.

  In the present embodiment, both ends of the belt reinforcing layer 17 are covered with the reinforcing cord layer 18, but the present invention is not limited to this configuration, and only one end of the belt reinforcing layer 17 is provided with the reinforcing cord. It is good also as a structure covered with the layer 18, and it is good also as a structure covered with the one reinforcing cord layer 18 which continues the both ends of the belt reinforcement layer 17 in a tire width direction. Further, the reinforcing cord layer 18 may be omitted depending on the specification of the tire 10.

  A tread portion 20 is provided on the outer side in the tire radial direction of the inclined belt layer 16, the belt reinforcing layer 17 and the reinforcing cord layer 18. The tread portion 20 is a portion that contacts the road surface during traveling, and a plurality of circumferential main grooves 21 extending in the tire circumferential direction are formed on the tread surface of the tread portion 20. Further, the tread portion 20 is formed with a not-shown width direction groove extending in the tire width direction. In addition, the shape and the number of the circumferential main grooves 21 and the width direction grooves are appropriately set according to performances such as drainage performance and steering stability required for the tire 10. Further, the circumferential main groove 21 of the present embodiment has a groove width of 6 mm or more.

  The tire side portion 22 extends in the tire radial direction, connects the bead portion 12 and the tread portion 20, and is configured to be able to bear a load acting on the tire 10 during run-flat travel.

  The tire side portion 22 is provided with a side reinforcing rubber layer 24 that reinforces the tire side portion 22 inside the carcass 14 in the tire width direction. The side reinforcing rubber layer 24 is a reinforcing rubber for running a predetermined distance while supporting the weight of the vehicle and the occupant when the internal pressure of the tire 10 decreases due to puncture or the like. Note that the side reinforcing rubber layer 24 of the present embodiment is an example of the side reinforcing layer of the present invention.

Moreover, in this embodiment, although the side reinforcement rubber layer 24 is formed with one type of rubber material, it is not limited thereto, and may be formed with a plurality of rubber materials. As long as the rubber material is a main component, the side reinforcing rubber layer 24 may include other materials such as fillers, short fibers, and resins. Further, a rubber material having a hardness of 70 to 85 may be included as a rubber material constituting the side reinforcing rubber layer 24 in order to enhance durability during run flat running. Furthermore, the loss coefficient tan δ measured by using a viscoelastic spectrometer (for example, a spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd.) at a frequency of 20 Hz, an initial strain of 10%, a dynamic strain of ± 2%, and a temperature of 60 ° C. is 0.10 or less. A rubber material having physical properties may be included. In addition, the hardness of rubber | gum here refers to the hardness prescribed | regulated by JISK6253 (type A durometer).
In the present embodiment, the side reinforcing rubber layer 24 mainly composed of rubber is used as an example of the side reinforcing layer of the present invention. However, the present invention is not limited to this, and other materials having rubber-like elasticity (for example, , A thermoplastic resin or the like) may be used as a main reinforcing layer.

  The side reinforcing rubber layer 24 extends in the tire radial direction along the inner surface of the carcass 14 from the bead portion 12 side to the tread portion 20 side. The side reinforcing rubber layer 24 has a shape that decreases in thickness as it goes from the central portion toward the bead portion 12 side and the tread portion 20 side, for example, a substantially crescent shape. Here, the thickness of the side reinforcing rubber layer 24 refers to the length along the normal line of the carcass 14 when the tire 10 is assembled to the standard rim 30 and the internal pressure is set to the standard air pressure.

  An inner liner (not shown) is disposed on the inner surface of the side reinforcing rubber layer 24 from one bead portion 12 to the other bead portion 12. In the present embodiment, as an example, an inner liner mainly composed of butyl rubber is disposed. However, the present invention is not limited thereto, and another rubber material or an inner liner mainly composed of resin may be disposed. .

  The side reinforcing rubber layer 24 has a lower end portion 24A on the bead portion 12 side overlapping the bead filler 28 with the carcass 14 interposed therebetween, and an upper end portion 24B on the tread portion 20 side overlapping the inclined belt layer 16 with the carcass 14 interposed therebetween. Yes. Specifically, the upper end portion 24B of the side reinforcing rubber layer 24 overlaps the belt ply 16A with the carcass 14 interposed therebetween. That is, the upper end portion 24B of the side reinforcing rubber layer 24 is located on the inner side in the tire width direction than the end portion 16AE of the belt ply 16A.

As shown in FIG. 1, in the tire 10, the outer side in the tire width direction of the outermost circumferential main groove 21 </ b> A in the tire width direction of the plurality of circumferential main grooves 21 from the end 16AE of the belt ply 16 </ b> A on the outer side in the tire width direction. The distance along the tire width direction to the opening edge 21AE is A [mm], the width of the belt ply 16A (the maximum width of the inclined belt layer 16) is B [mm], and the groove depth of the circumferential main groove 21A is When C [mm] is satisfied, A / B> 0.025 × C + 0.06... Satisfies the relationship of the formula (1).
In addition, the groove depth C of the circumferential main groove 21A here refers to the length along the normal direction of the tread surface from the opening edge 21AE to the groove bottom (deepest part).
Moreover, 0.025 of Formula (1) is a coefficient (unit [1 / mm]) of the groove depth C, and 0.06 is a constant term.

  Moreover, in this embodiment, since the tire 10 with the high tire cross-section height SH is targeted, the rim guard (rim protection) is not provided, but the present invention is not limited to this configuration, and a rim guard may be provided.

  Next, the effect | action of the tire 10 of this embodiment is demonstrated.

  First, the rim disengagement mechanism of the run flat tire will be briefly described. Here, it demonstrates using the tire (illustration omitted) of the comparative example which is the structure same as the tire 10 except the point which does not satisfy | fill Formula (1). When SA (slip angle) is given to the tire of the comparative example, for example, by turning during run-flat running, the ground contact portion of the tire of the comparative example is crushed and the amount of deflection increases, and the belt diameter of the stepping portion increases. As a result, the tensile force on the outer side in the tire radial direction with respect to the bead portion located on the inner side of the turn increases at the stepping position, and the bead portion is standard, coupled with the buckling generated at the stepping position of the tire side portion located on the inner side of the turn of the vehicle. There is a detachment from the rim.

  By the way, as shown in FIG. 3, it has been confirmed that the rim disengagement inside the turning of the vehicle is likely to occur in a tire having a tire cross-section height SH of 115 mm or more. The graph shown in FIG. 3 is obtained by examining the rim detachment index with respect to the tire cross section height SH using a run flat radial tire having a tire width of 215 mm and the tire cross section height SH being changed. The larger the is, the harder it is to remove the rim. According to FIG. 3, in the case of a tire having a tire cross-section height SH smaller than 115 mm, the rim on the turning outer side of the tire is easily detached, and in a tire having a tire cross-section height SH of 115 mm or more, the turning inner side It can be seen that it is important to prevent the rim from coming off. Note that the tire cross-section height is specifically 250 mm or less, particularly 155 mm or less.

  Here, in the tire 10 of the present embodiment, the distance A [mm], the width B [mm], and the groove depth C [mm] satisfy the relationship of the formula (1), for example, the relationship of the formula (1). As compared with a tire of a comparative example that does not satisfy the above, the bending rigidity in the vicinity of the tread end portion T that becomes the starting point of the buckling phenomenon is increased. In addition, the tread end part T vicinity here includes the tread end part T side of the tread part 20 and the tread end part T side of the shoulder part 22B. As a result, as shown in FIG. 2, even when SA is applied during run-flat running, the vicinity of the tread end T is difficult to bend, and the tire side portion located inside the turning of the vehicle starting from the vicinity of the tread end T The occurrence of a buckling phenomenon can be suppressed in FIG. As a result, the occurrence of the phenomenon that the bead portion 12 is detached from the standard rim 30 (rim removal) is suppressed. That is, according to the tire 10, it is possible to suppress the occurrence of a buckling phenomenon in the tire side portion 22 and to improve the rim detachment resistance during run-flat traveling.

  Further, in the tire 10, since the upper end portion 24B of the side reinforcing rubber layer 24 is overlapped with the belt ply 16A, the rigidity in the vicinity of the tread end portion T is improved and the occurrence of the buckling phenomenon of the tire side portion 22 can be further suppressed.

  Here, when the upper end portion 24B of the side reinforcing rubber layer 24 is overlapped with the belt ply 16A, the tread portion 20 bends in the tire width direction starting from the groove bottom of the circumferential main groove 21A during run flat travel (during straight travel), An excessive tensile force may act on the inner surface of the side reinforcing rubber layer 24 corresponding to the vicinity of the end 16AE of the belt ply 16A. However, when the relationship of (Formula 1) is satisfied, the distance A from the end portion 16AE of the belt ply 16A to the opening edge portion 21AE of the circumferential main groove 21A and the groove depth C of the circumferential main groove 21A are regulated. Therefore, the tread portion 20 is less likely to bend in the tire width direction starting from the groove bottom of the circumferential main groove 21A (bending is suppressed), and the inner surface of the side reinforcing rubber layer 24 corresponding to the vicinity of the end portion 16AE of the belt ply 16A It is possible to suppress an excessive tensile force from acting on the surface. Accordingly, it is possible to improve the durability of the side reinforcing rubber layer 24 during the run-flat running while suppressing the occurrence of the buckling phenomenon of the tire side portion 22.

  As described above, even if the tire cross section height (section height) is 115 mm or more, the distance A [mm], the width B [mm], and the groove depth C [mm] are in the relationship of the formula (1). By satisfy | filling, it can suppress effectively that a buckling phenomenon generate | occur | produces in the tire side part 22. FIG.

  The embodiments of the present invention have been described above with reference to the embodiments. However, these embodiments are merely examples, and various modifications can be made without departing from the scope of the invention. It goes without saying that the scope of rights of the present invention is not limited to these embodiments.

(Test example)
In order to confirm the effects of the run-flat radial tire according to the present invention, the following run-flat radial tires of Examples 1 to 5 and the run-flat radial tires of Comparative Examples 1 to 4 that are not included in the present invention are prepared. The test was conducted.

  First, the run flat radial tires of Examples 1 to 3 and the run flat radial tires of Comparative Examples 1 and 2 used in Test 1 will be described. The run-flat radial tires of Examples 1 to 3 and Comparative Examples 1 and 2 are tires having a size of 215 / 60R17 adopting the same structure as the tire (10) shown in FIG. These test run flat radial tires have an opening edge of the circumferential main groove (21A) at the outermost side in the tire width direction from the end (16AE) of the belt ply (16A) with respect to the width B [mm] of the belt ply (16A). The ratio Y [%] of the distance A [mm] along the tire width direction to the portion (21AE) and the groove depth C [mm] of the circumferential main groove (21A) are different. The ratio Y [%] is a numerical value obtained by (distance A [mm] / width B [mm]) × 100 [%]. The numerical values of Examples 1 to 3 and Comparative Examples 1 and 2 are as shown in Table 1.

  In Test 1, first, a test run-flat radial tire was assembled on a standard rim of JATMA standard, mounted on the vehicle without filling with air (with an internal pressure of 0 kPa), and habituated to a distance of 5 km at a speed of 20 km / h. Ran. After that, entering a turning circuit having a radius of curvature of 25 m at a predetermined speed and stopping at a position of 1/3 turn of this turning circuit was performed twice in succession (J-turn test). This J-turn test was carried out while increasing the approach speed by 2 km / h, and the turning acceleration when the bead part was detached from the rim (rim hump) was measured. Here, with reference to the turning acceleration when the bead portion of Comparative Example 2 is detached from the rim as a reference value (100), the turning acceleration when each bead portion of Examples 1 to 3 is detached from the rim is shown in Table 1. It was expressed as an index in the “Index” column. The “rim detachment index” in Table 1 is an index that represents the turning acceleration when the bead part is detached from the rim. The larger the value, the better the result (the result that the rim is less likely to detach). .

  As shown in Table 1, the run-flat radial tires of Examples 1 to 3 have a better rim detachment index than the run-flat radial tires of Comparative Examples 1 and 2. This is probably because the run-flat radial tires of Examples 1 to 3 all satisfy the above-described formula (1), and the occurrence of the buckling phenomenon in the tire side portion is suppressed. Note that the straight line L in the graph of FIG. 4 is an expression of a ratio Y [%] = (0.0625 [1 / mm] × C [mm] +0.06) × 100 [%] based on the expression (1). The run flat radial tires of Examples 1 to 3 that are obtained above the straight line L are better than the comparative examples 1 and 2 that are located below the straight line L with respect to the buckling of the tire side portion. Is shown.

  Next, the run-flat radial tires of Examples 4 and 5 and the run-flat radial tires of Comparative Examples 3 and 4 used in Test 2 will be described. These test run flat radial tires are tires having a size of 215 / 60R17. Further, the run-flat radial tire of Example 5 adopts the same structure as the tire (10) shown in FIG. On the other hand, although Example 4 satisfy | fills the relationship of Formula (1), the upper end part (24B) of a side reinforcement rubber layer (24) is a tire width direction rather than the edge part (16AE) of a belt ply (16A). In other words, the upper end portion (24B) of the side reinforcing rubber layer (24) does not overlap the belt ply (16A) in the tire width direction. Further, Comparative Examples 3 and 4 do not satisfy the relationship of Formula (1), but in Comparative Example 4, the upper end portion (24B) of the side reinforcing rubber layer (24) is in the tire width direction to the belt ply (16A). It is set as the structure which overlaps, and the comparative example 3 is set as the structure which does not overlap.

In Test 2, first, a J-turn test was performed on the test run-flat radial tire under the same conditions as in Test 1, and the turning acceleration of Comparative Example 3 was set as the reference value (100). The turning acceleration of Example 4 was expressed as an index in the column of the rim removal index in Table 2. Note that the “rim detachment index” in Table 2 indicates a better result (a result that rim detachment is difficult) as the value is larger, as in Test 1.
Next, the test run flat radial tire is assembled to the standard rim, attached to the drum testing machine without filling with air (with an internal pressure of 0 kPa), and pressed against the rotating drum with a predetermined radial load. While running at a speed (rotational speed), running distance (running on a rotating drum) until a failure occurs on the inner surface of the side reinforcing rubber layer of each test run-flat radial tire while running flat (run-flat straight running) Distance) was measured. And when the failure occurred on the inner surface of each side reinforcing rubber layer of Examples 4, 5 and Comparative Example 4, with the running distance until the inner surface of the comparative example 3 side reinforcing rubber layer failed as a reference value (100) The mileage is shown as an index in the “Run-flat durability” column of Table 2. In addition, “run-flat durability” in Table 2 is an index representing the distance traveled until a failure occurs on the inner surface of the side reinforcing rubber layer. Moreover, regarding the numerical value of run flat durability, the larger the value, the better the result.

  As shown in Table 2, the run-flat radial tire of Example 5 has a better rim removal index and run-flat durability than the run-flat radial tires of Comparative Examples 3, 4 and Example 4. . This is because the run-flat radial tire of Example 5 satisfies the relationship of the above-described formula (1), and the end portion on the bead portion side of the side reinforcing rubber layer is on the inner side in the tire width direction than the end portion on the outer side in the tire width direction. Because it is positioned (it overlaps the belt ply with the maximum width in the tire width direction), the occurrence of buckling phenomenon on the tire side is suppressed, while the durability of the side reinforcement layer during run flat running is suppressed. It seems that it was because of

DESCRIPTION OF SYMBOLS 10 Run flat radial tire 12 Bead part 14 Carcass 16 Inclined belt layer 16A Maximum width belt ply 16AE End part 20 Tread part 21 Circumferential main groove 21A Outermost circumferential main groove in the tire width direction 22 Tire side part 24 Side reinforcement rubber Layer SH Tire cross-section height A Distance B Belt ply width C Groove depth

Claims (3)

A carcass straddling between a pair of bead parts;
An inclined belt layer formed of at least one belt ply provided with a cord provided on the outer side in the tire radial direction of the carcass and extending in a direction inclined with respect to the tire circumferential direction;
A tread portion provided on the outer side in the tire radial direction of the inclined belt layer, and a plurality of circumferential main grooves extending in the tire circumferential direction on the tread surface;
A side reinforcement layer provided on a tire side portion that connects the bead portion and the tread portion, is located on the tire inner side of the carcass, and extends from the bead portion side to the tread portion side to reinforce the tire side portion. When,
Have
A distance in the tire width direction from the outer end portion of the belt ply of the maximum width in the tire width direction to the opening edge portion of the circumferential main groove on the outermost side in the tire width direction on the outer side in the tire width direction is A [mm], When the width of the belt ply having the maximum width is B [mm] and the groove depth of the circumferential main groove on the outermost side in the tire width direction is C [mm], A / B> 0.025 × C + 0.06 Run-flat radial tires that satisfy the relationship.   2. The run-flat radial tire according to claim 1, wherein the side reinforcing layer has an end on the tread portion side positioned on an inner side in the tire width direction of an end portion on the outer side in the tire width direction of the belt ply having the maximum width. .   The run-flat radial tire according to claim 1 or 2, wherein a tire cross-section height is 115 mm or more.